(1) Field of the Invention
The present invention pertains to beam mode discharge fluorescent lamps and more particularly to an arrangement for configuring the cathode within a beam mode discharge fluorescent lamp.
(2) Description of the Prior Art
U.S. patent application Ser. No. 219,564, filed on Dec. 23, 1980, now abandoned for a "Beam Mode Fluorescent Lamp", and assigned to the same assignee as the present invention, discloses a particular embodiment of a fluorescent lamp suitable for replacing the conventional incandescent bulb. Although incandescent lamps are inexpensive and convenient to use, they are considerably less efficient than fluorescent lamps.
In the above mentioned patent application, a single anode and cathode configuration is shown. A discharge is formed between the electrodes and electrons are emitted. Ions in the cathode potential drop region are accelerated by the field and bombard the cathode. This ion bombardment is not uniform and concentrates at the most negative end of the cathode. This leads to severe localized heating of the cathode with an elevated primary electron emission. The localized heating produces evaporation of the cathode coating with a resultant shortening of cathode life and darkening of the phosphor coating and increased chance of discharge "runaway" and cathode "burn-out".